The field of the present invention involves use of optical fiber to convey light from a source thereof over a distance so as to achieve illumination of a surface therewith. Further, the present invention involves introduction of a coherent collimated laser beam into a first end of an optical fiber wherein multimodal propagation of the laser light occurs, and formation of laser light issuing from the opposite end of the optical fiber into an apparently collimated projectable beam. Because the apparently collimated beam is projectable with known characteristics, it may be advantageously employed to effect controlled illumination by projection over an additional known distance.
Use of optical fiber to convey laser light is known in the telecommunications technology. These known uses generally involve generation of a modulated laser light beam, for example, from a laser diode, and introduction of the modulated beam into an optical fiber. At the opposite end of the fiber the modulated light beam is directed upon a photo diode, or other photo-sensitive detector, for reconversion to an electrical signal. Because laser diodes and photo diodes are relatively large devices in comparison with the diameter of the optical fiber, common practice is to employ fibers having a rather large numerical aperture. The numerical aperture (hereinafter N.A.) of an optical fiber is the sine of one-half the divergence angle is air of light issuing from the outlet end of the optical fiber. Thus, use of optical fibers with a rather large N.A. is advantageous in telecommunications technology because they have both a large acceptance cone at their input end for receipt of light from a large laser diode, and produce a widely divergent (not collimated) beam for illumination of a photo diode at the opposite end of the fiber. A result of this coupling of optical fibers both with laser or photo diodes, and with other like optical fibers, has been the increasing acceptance of interface optics employing a full spherical lens, or a lens appearing optically as though it were full-spherical. However, the applications employing full-spherical or pseudo-spherical lenses as interface optics with an optical fiber do not anticipate projection over a substantial distance of a beam of light conveyed by the optical fiber.
The following U.S. Patents and other documents are believed to set forth teachings relating to use of optical fibers in telecommunications. These teachings were located by a pre-filing patentability search conducted on behalf of the Applicants, or are otherwise known to them at the time of filing.
______________________________________ U.S. Pat. No. Inventor U.S. Pat. No. Inventor ______________________________________ 3,656,832 Judin 4,329,017 Kapany et al 4,119,362 Holzman 4,380,365 Gross 4,183,618 Rush et al 4,420,219 Muchel 4,199,222 Ikushima et al 4,421,383 Carlsen 4,257,672 Balliet 4,483,585 Takami 4,273,109 Enderby 4,456,812 Neiheisel et al 4,290,667 Chown 4,531,810 Carlsen 4,327,963 Khoe et al 4,563,057 Ludman et al Great Britain Patent 2,120,400 German Patent DE 3224631 ______________________________________ Publications: L. G. Cohen, M. V. Schneider, "Microlenses for Coupling Junction Lasers to Optical Fibers", APPLIED OPTICS, Vol. 13, No. 1, January 1974, pp. 89-94. N. Nager, "Glass Sphere Lenses For Better Coupling", PHOTONICS SPECTRA, September 1983. D. E. Welsh, P. Popper, "Optical Contacts", Malco-South Pasadena, 306 Pasadena Avenue, South Pasadena, CA 91030.
However, communication of laser light via optical fiber also has present or potential application in many fields including laser machining operations of various types, for example, welding, drilling and cutting; in laser catheters used for in vivo surgery; and in scanning laser light projections for producing visual effects and displays. In laser machining, for example, conventional practice requires the laser and workpiece to be precisely moved relative one another in order to apply the laser light directly from the laser to various locations on the workpiece. Fiber optic applications to laser machining are believed to employ a relatively stationary laser and workpiece with a projection head which is movable relative to the workpiece. The projection head is coupled with the laser via optical fiber to receive and project the laser light. However, heretofore, such fiber optic coupling and projection apparatus have suffered from low efficiency and poor quality of the projected laser beam.
Also, in the field of laser light projections for producing visual displays by scanning the laser light upon a surface, use of fiber optics to convey the laser light to a projection head having movable mirrors therein for scanning the beam has also encountered previously insurmountable difficulties. These difficulties are similar to those encountered in laser machining and include low transmission efficiency and poor quality of the projected beam.
Many of the above difficulties in use of optical fiber to convey light are known to originate with the light propagation characteristics of the optical fiber itself. That is, a laser beam issuing from a gas discharge laser, for example, is coherent and collimated. However, when this laser beam is condensed and introduced into an optical fiber, the beam issuing from the opposite end of the fiber is divergent rather than collimated. Additionally, the beam issuing from the fiber may be single mode if the fiber propagates only the transverse electromagnetic (0,0) (TEM.sub.00) mode, or may appear with two or more modes. In the cases having two or more modes issuing from the fiber output end, projection of the beam through projection optics is particularly difficult because each mode is manifest as a different projected beam pattern. That is, the projected beam of one mode may be an annulus (TEM.sub.01), while another mode produces a pair of spots side by side, for example. Of course, for the applications of interest, such as laser machining and laser optical displays, a beam projected over a substantial distance as a sharply-defined single spot is desired
Another difficulty encountered when optical fiber is employed with a laser is in aligning the laser, a concentrating optic, and the fiber end so that the laser beam is properly introduced into the fiber core. Heretofore, such alignment required use of an optical bench and resulted in assemblies which were either frail and required frequent readjustment, or which were permanently united. Of course, when a permanently united assembly received some damage the entire unit most likely was unusable because no part thereof could be replaced. No conventional apparatus or method was available to provide interchangeable components which were both properly aligned optically, and truly interchangeable so that only a damaged or worn component of an entire assembly could be replaced.